In a wireless communication system, mutual interference exists among signals of different users, and in a Gaussian interference channel, each user knows respective complete channel information, but data of different users cannot be shared, so joint transmission cannot be performed. As shown in FIG. 1, a Gaussian interference channel of two users is shown, and interference exists between users x1 and x2. How to improve the capacity of the Gaussian interference channel when eliminating the interference among the users is always one of main bottlenecks limiting the development of the technology.
A conventional solution of avoiding mutual interference among users in an interference channel adopts orthogonalization, such as a time division multiple address (TDMA) technology and a frequency division multiple address (FDMA) technology. As shown in FIG. 2, a schematic diagram of a TDMA system is shown. In the TDMA system, different users send data at different time, thereby avoiding mutual interference among the users. Similar to the TDMA system, in the FDMA system, different users send data at different frequencies, thereby also avoiding mutual interference among the users.
In view of the defects in the conventional solution, along with the intensive study on the Gaussian interference channel, a method for solving mutual interference among users by using interference alignment is proposed. The interference alignment refers to that, in the situation of knowing complete channel information, through preprocessing of a transmitting end, a useful signal and an interference signal of each receiving end are separated in space, and the interferences of different transmitting ends to the receiving end are all aligned to the same spatial dimension, thereby avoiding the influence of the interference and achieving the objective of improving the capacity. The research on the capacity of the Gaussian interference channel and the interference alignment are still in a primary stage, so the method of interference alignment is currently a hotspot in researching.
The prior art provides an example of interference alignment in a special channel. As shown in FIG. 3, the special channel includes K transmitting ends and K receiving ends. A channel response of each transmitting end to a target receiving end is 1, and an interference channel of each transmitting end to all users is correspondingly i, and if a transmission signal is a real part of a signal space, a receiving signal at a kth receiving end is:
                              r          k                =                              s            k                    +                      i            ⁢                                          ∑                                                      l                    =                    1                                    ,                                      l                    ≠                    K                                                  K                            ⁢                                                          ⁢                              s                l                                              +                      n            k                                              (        1        )            
Obviously, the receiving end can detect the transmission signal only by directly obtaining the real part of the receiving signal, that is,
                              Re          ⁡                      (                          r              k                        )                          =                              Re            ⁡                          (                                                s                  k                                +                                  i                  ⁢                                                            ∑                                                                        l                          =                          1                                                ,                                                  l                          ≠                          K                                                                    K                                        ⁢                                                                                  ⁢                                          s                      l                                                                      +                                  n                  k                                            )                                =                      Re            ⁡                          (                                                s                  k                                +                                  n                  k                                            )                                                          (        2        )            
It can be seen that, although the transmission signal losses a half of the signal space, the interference among the users is eliminated.
In the prior art, a method of explicit interference alignment (Explicit IA) is further provided, and in the situation that three users have the same antenna, the Explicit IA method includes constructing the following relationship in a column space (C) first:c(H(12)V(2)=c(H(13)V(3)),c(H(H(21)V(1))=c(H(23)V(3)),c(H(31)V(1))=c(H(32)V(2)).
where, H(ij) represents a channel coefficient matrix from a transmitter j to a receiving end i. V(i) represents a pre-coding matrix of a transmitting end i. The following expressions may be obtained according to the foregoing formula:E=(H(31))−1H(32)(H(12))−1H(13)(H(23))−1H(21),F=(H(32))−1H(31) and G=(H(23))−1H(21),
Therefore, the matrix constructed by using the first half eigenvector of the matrix E as a row vector is used as a pre-coding matrix V(1) of a transmitting end 1; and pre-coding matrices v(2) and V(3) of a transmitting end 2 and a transmitting end 3 are obtained respectively as follows:V(2)=FV(1),V(3)=GV(1) 
During the implementation of the present invention, the inventor finds that the prior art at least has the following problem: the conventional orthogonalization solution such as TDMA and FDMA results in an excessively low capacity of the system, which is only 1/K log(SNR)+o(log(SNR)), thereby limiting the throughput of the system. As for the conventionally provided interference alignment method, it is only applicable to a certain special channel, the special channel is difficult to be constructed and can hardly be implemented, and the method has high bit error rate and poor performance.